FIG. 1 shows a sleeve 2 and spool 4 of a conventional spool valve where the sleeve has ports 6 and spool has annular seals 8 compressed against inner peripheral wall 10 of sleeve 2. Ports 6 are typically drilled holes having sharp edges 12 at inner wall 10, edges tend to cut or otherwise damage seals 8 as these seals pass the ports. The interaction of seals 8 with edges 12 is seen in FIGS. 2 and 2A. Counterbored holes 14 (FIG. 2B) are often used to reduce seal damage in spool valves. Counterbore 16 of hole 14 is cut by a tool inserted axially through sleeve 2, the tool having a radially oriented cutting head aligned with hole 14. Machining a counterbore by this method is feasible but is relatively slow and expensive.